S under acidic conditions. M. tuberculosis does not grow at pH 5.5 (Vandal et al., 2009a), and releases large amounts of ammonia in excess of 5 mM to increase the pH to 6.5 before it enters the exponential growth phase (Fig. 5). This is within the physiologically relevant pHNIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptMol Microbiol. Author manuscript; available in PMC